Stretchable cryoprobe sheath

ABSTRACT

A sheath for use on a closed loop Joule-Thomson cryosurgical probe, and the combination of the sheath and the closed loop probe. The sheath is slipped over the probe, thereby separating the probe from the environment. The sheath has a grip which fits over the handle of the cryosurgical probe, and an extendible shroud which can be longitudinally extended to cover tubing and which are attached to the handle. The sheath has a hollow multi-lumen catheter shaped and sized to fit snugly over the cannula of the cryosurgical probe. The catheter is not thermally conductive, preventing transfer of heat from the ambient to the gas mixture, and preventing the freezing of tissues at undesired locations along the catheter. A thermally conductive cap or tip is attached to the distal end of the hollow catheter. The thermally conductive cap or tip is biased against the cold tip on the probe by a biasing element in the sheath assembly, to promote heat transfer.

CROSS REFERENCE TO RELATED APPLICATIONS

This is a continuation-in-part patent application of U.S. patentapplication Ser. No. 09/262,588, filed on Mar. 4, 1999, and entitled“Cryosurgical Probe with Sheath”, now U.S. Pat. No. 6,193,644 and ofU.S. patent application Ser. No. 08/774,148, filed on Dec. 26, 1996, andentitled “Cryosurgical Probe with Disposable Sheath”, now U.S. Pat. No.5,910,104.

FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

Not Applicable

BACKGROUND OF THE INVENTION

The present invention is in the field of cryosurgical probes used forfreezing and thereby destroying biological tissues. More specifically,the present invention is useful in the field of cryosurgical probeswhich are cooled by a closed loop Joule-Thomson refrigeration system.

A Joule-Thomson refrigeration system operates by expanding a highpressure gas through an expansion element which incorporates some sortof a flow restriction. The flow restriction might be a small orifice, anarrow capillary tube, or some other sort of restricted passageway.Typically, the refrigeration system includes a source of high pressuregas, a heat exchanger, an expansion element, a heat transfer element,and various tubes or conduits to conduct the gas from one component toanother. The high pressure gas passes through the heat exchanger tolower the gas temperature somewhat, then the gas temperature is furtherlowered in the expansion element, as isenthalpic expansion occurs. Theexpanded, cooled gas is exposed to the heat transfer element, where thegas absorbs heat which has been transferred from the environment. Theoperation of a Joule-Thomson refrigeration system can be severelyaffected by contaminants in the gas, such as water, oil, orparticulates. Any such contaminant can easily block the flow restrictionin the expansion element, because the flow restriction is typically verysmall.

Water and oil are particularly detrimental contaminants, because theywill selectively collect at the flow restriction, where the majority ofthe cooling occurs. As the gas expands and cools, the temperature ofentrained water and oil also lowers, resulting in the freezing orsolidification of the water and oil. This solidification occurs exactlyat the flow restriction, because that is where the cooling actuallyoccurs. Water and oil, at least in trace amounts, are often found inambient air, and they can consequently be introduced into therefrigeration system if any system joints are broken or any system partsare replaced.

Most Joule-Thomson systems are open loop, meaning that the gas isexhausted to the atmosphere after expansion and heat absorption. Thesource of the high pressure gas in such a system is usually a highpressure gas cylinder. As use proceeds, the amount of gas in thecylinder is depleted. An open loop system such as this can tolerate acertain amount of contamination, because the contaminants are exhaustedfrom the system to the environment along with the gas, during use. Ifany contamination is introduced into the system during the replacementof parts, or when system joints are broken for other reasons, thecontamination is largely flushed out as the gas is subsequentlyexhausted.

However, it is possible to operate a closed loop Joule-Thomson system,meaning that the gas is repressurized and circulated after expansion.After expansion in the expansion element, exposure to the heat transferelement, and absorption of heat, the low pressure gas is returned to acompressor which can be used to repressurize the gas. The repressurizedgas is then circulated back through the heat exchanger and the expansionelement. None of the gas is exhausted from the system. Therefore, anycontaminants which enter the system are collected in the system, wherethey accumulate over a period of time. The level of contamination caneventually build up to a level where solidification of the water and oilwill plug the expansion element. A method and apparatus have beendeveloped for operating a micro-miniature mixed-gas Joule-Thomsonrefrigeration system, as disclosed in U.S. patent application Ser. No.08/542,123, filed Oct. 12, 1995, and U.S. patent application Ser. No.08/698,044, filed Aug. 15, 1996, which are incorporated herein forreference. If such a mixed-gas is used, especially in a miniature ormicro-miniature refrigeration system, the introduction of air into thesystem alters the gas mixture ratios, and it can significantly detractfrom the cooling performance of the gas mixture.

For these reasons, closed loop Joule-Thomson systems are oftenpermanently sealed, to prevent the introduction of contaminants.Replacement of parts, or other breaking of system joints, is notpossible in a permanently sealed system. Some systems use self sealingcouplings, which automatically close the system when they are brokenapart. This automatic sealing limits the amount of leakage andcontamination, but some contamination still occurs. Typically, thecouplings used in a closed loop system are threaded fittings which arenot designed for repetitive disconnection.

The contamination problem becomes more complicated in a closed loopmixed-gas Joule-Thomson refrigeration system which is used in a surgicaldevice, such as a cryosurgical probe. Such a device will typically havea compressor hooked to the probe, with the probe consisting essentiallyof a handle, a cannula, and a cold tip. The heat exchanger is typicallylocated in the handle, and the expansion element is typically located inthe cold tip. The probe cannula or cold tip must be interchangeable withvarious shapes, such as flat, cylindrical, or sharp edged, to performdifferent functions. Further, the cold tip must be capable of beingsterilized for use in a surgical application, to allow repeated use ofthe system on different patients.

Known cryosurgical probes are open loop systems for this reason. In anopen loop system, the cannula or cold tip can be removed and sterilizedor discarded. Introduction of contaminants into the refrigeration systemduring removal and replacement of the cannula or cold tip is not asignificant problem in an open loop system, since the contaminants canbe flushed from the system during exhaust of the gas. Open loop systemsare wasteful and expensive to operate, because of the necessity ofcontinually replacing the gas. Also, exhaust of the gas to theenvironment is not always environmentally safe. Closed loop systems aremore economical and environmentally safe. If a known closed loop systemwere used in a surgical application, removal and replacement of thecannula or cold tip for sterilization purposes would introducecontaminants into the system, ultimately resulting in blockage of theexpansion element. A closed loop surgical system could theoretically beprovided with self sealing couplings, but contamination would stillbuild up over a period of time. Further, self sealing couplingsincorporate O-rings and precision parts. Sterilization of the cannula orcold tip would inevitably expose the O-rings and precision parts to hightemperatures and harsh chemicals, ultimately resulting in degradation ofthe sealing ability of the couplings.

Use of disposable replacement cannulas or cold tips would not solve thisdilemma. First, even if the replaceable parts are discarded and replacedwith new, sterile parts, repetitive disconnections are required,ultimately resulting in the buildup of contaminants. Second, mostdisposable parts are constructed of plastic, for reasons of economy.Plastics typically contain trace amounts of water. If a plastic part isexposed to the gas in a refrigeration system, the water can eventuallyleech out of the plastic and contaminate the gas in the system. Third,self sealing fittings typically add size, weight, and significant costto a device, making them undesirable for use in a disposable device.Fourth, each time a disposable element, such as a cannula or cold tip,is discarded, the refrigerant gas contained within the disposableelement is lost. This requires replacement of the gas to avoiddegradation of the cooling performance of the system. Evacuation of gasfrom the disposable component, or use of replacement componentsprecharged with gas, would significantly add to the complexity and costof the system.

Further, a typical cryosurgical probe will have one or more auxiliaryinstruments near the cold tip, for use in conjunction with the cold tip,such as temperature sensors, heaters, ultrasound transducers, opticalelements, and fluid ports for irrigation and aspiration. If a reusableprobe is employed, repetitive sterilization of these auxiliaryinstruments can degrade their performance. The ideal practice would beto incorporate these auxiliary instruments into a disposable element.

Finally, it is desirable to insulate the shaft of a cryosurgical probe,to prevent freezing of tissue at undesired sites along the probe whenthe probe is inserted into a body cavity or organ. One effective meansof insulation would be to provide a vacuum space along the probe shaft.However, the level of the vacuum maintained in such a space can degradeover time, because of the outgassing of metals, plastics, and brazejoints. This outgassing increases during sterilization procedures inwhich heat is applied to the probe. Therefore, it would be desirable toincorporate the vacuum insulation space into a disposable element Thedisposable element would only be sterilized once, and the disposableelement can then be economically discarded, minimizing the amount ofvacuum degradation.

BRIEF SUMMARY OF THE INVENTION

The present invention is a sheath for use on a closed loop Joule-Thomsoncryosurgical probe, and the combination of the sheath and the closedloop probe. The sheath is sufficiently flexible to be slipped over theprobe, thereby separating the probe from the environment and allowinguse of the probe in a surgical application. The sheath has a grip whichattaches to the handle of the cryosurgical probe, and an extendibleshroud attached to the proximal end of the grip. The shroud can belongitudinally extended to cover the refrigerant tubing andinstrumentation cables which are attached to the handle, therebyproviding a sterile barrier for these components.

The sheath also has a hollow multi-lumen catheter assembly consisting ofa catheter and a connector body. The catheter is attached to the distalportion of the grip, by the connector body, with at least one lumenbeing shaped and sized to fit snugly over the cannula of thecryosurgical probe. The catheter is not thermally conductive, so itassists in preventing transfer of heat from the ambient to the gasmixture, and preventing the freezing of tissues at undesired locationsalong the catheter. A thermally conductive segment is attached to thedistal end of the catheter, in the form of a metal cap or tip. The metaltip can be round, flat, sharp, or any other shape suitable for thecryosurgical operation being performed. The thermally conductive cap ortip fits over the cold tip on the probe. A biasing element in thecatheter assembly biases the conductive tip of the sheath proximallyagainst the cold tip on the probe. This causes the conductive segment onthe catheter to efficiently transfer heat from the target tissue to thecold tip, which in turn transfers heat to the expanded gas mixture.

The novel features of this invention, as well as the invention itself,will be best understood from the attached drawings, taken along with thefollowing description, in which similar reference characters refer tosimilar parts, and in which:

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an elevation view of a cryosurgical probe of the type whichmight be used in the present invention;

FIG. 2A is an elevation view of a sheath according to the presentinvention;

FIG. 2B is an elevation view of an alternative embodiment of the sheathaccording to the present invention;

FIG. 2C is a distal end view of the alternative embodiment of the sheathshown in FIG. 2B;

FIG. 3 is an elevation view of a sheath in place over a cryosurgicalprobe, according to the present invention;

FIG. 4 is a schematic view of a cryosurgical probe as shown in FIG. 1;

FIG. 5 is a section view of the proximal portion of the sheath as shownin FIG. 2A;

FIG. 6 is a distal end view of the cryosurgical probe as shown in FIG.1;

FIG. 7 is an elevation view of the proximal portion of the sheath ofFIG. 1, with the shroud furled;

FIG. 8 is a section view of the proximal portion of the sheath of FIG.7, with the shroud furled;

FIG. 9 is a longitudinal section view of the proximal portion of theconnector body of the sheath;

FIG. 10 is a longitudinal section view of the distal portion of theconnector body of the sheath;

FIG. 11 is a transverse section view of the distal portion of theconnector body of the sheath;

FIG. 12A is a transverse section view of the catheter of the sheathinstalled on the cannula of the cryosurgical probe;

FIG. 12B is a transverse section view of an alternate embodiment of thecatheter of the sheath, incorporating a vacuum jacket, installed on thecannula of the cryosurgical probe;

FIG. 13 is an elevation view of the distal end of the catheter of thesheath;

FIG. 14 is a longitudinal section view of the distal end of the catheterof the sheath;

FIG. 15 is a longitudinal section view of another embodiment of thesheath according to the present invention; and

FIG. 16 is a partial longitudinal section view of a portion of thesheath shown in FIG. 15.

DETAILED DESCRIPTION OF THE INVENTION

The present invention addresses the use of a sheath on a cryosurgicalprobe which operates on a closed loop mixed gas Joule-Thomsonrefrigeration system. Such a cryosurgical probe 10 is shown in FIG. 1.The probe 10 consists mainly of a handle 12, a hollow tubular cannula14, and a cold tip 16. The handle 12 can be metallic, to facilitateeffective sealing. The handle can have end caps vacuum brazed to thehandle cylinder, to hold a vacuum inside the handle 12, therebyproviding insulation. Alternatively, the handle 12 could be packed withinsulating material, such as aerogel. Several components of therefrigeration system, such as a heat exchanger, can be housed within thehandle 12, along with various auxiliary instrumentation to support itemssuch as temperature sensors, heaters, illumination optics, viewingoptics, laser optics, and ultrasonic transducers. An umbilical cord 18extending from the proximal portion of the handle 12 can contain tubingfor the refrigeration system, power cables for the electricalcomponents, or fiber optical cables to support the illumination,viewing, and laser components.

Other components of the refrigeration system, such as a high pressureconduit to transport a high pressure gas mixture from the probe handle12 to the cold tip 16, and a low pressure conduit to return the expandedgas mixture from the cold tip 16 to the probe handle 12, can be housedin the hollow cannula 14. Still other components of the refrigerationsystem, such as a Joule-Thomson expansion element, can be housed in thecold tip 16. The hollow cannula 14 is usually designed to minimize heattransfer from the surrounding tissues to the cryogenic gas mixture. Itcan be formed of a thermally resistive material, such as a rigidplastic, or it can be formed of a metal, with insulation appliedinternally or externally to inhibit heat transfer. The cannula 14 can bea rigid tube as shown, or it can be more flexible and shapeddifferently, depending upon the application. The cold tip 16 is a heattransfer element designed to maximize heat transfer from the targettissues to the expanded gas mixture. It can be formed of a thermallyconductive material, such as a metal, preferably silver. The cold tip 16can be a cap shaped element on the distal end of the cannula 14 asshown, or it can have another shape and be placed elsewhere on thecannula 14, depending upon the application. A plurality of grooves 17are formed in the cold tip 16 to allow the flow of thermal grease as thecold tip 16 is fitted inside the disposable sheath. Since thecryosurgical probe 10 is used with a closed loop refrigeration system,it will necessarily be sealed to prevent contamination. It may havebreakable joints which allow for replacement of parts, but any suchjoints will necessarily have sealing components which are not suitablefor normal sterilization procedures.

FIG. 2A shows a sheath 20 for disposition over the probe 10, to allowuse of the probe 10 in a protected environment without degradation ofthe effectiveness of the probe 10. Optionally, the sheath 20 can be madeof materials that are sterilized easily, and it can be constructedcheaply enough to be disposable. The sheath 20 includes a grip 22 whichfits over the probe handle 12, preferably with corrugations or othersurface features to provide a secure feel for the surgeon. An extendibleshroud 23 is attached to or formed on the proximal portion of the grip22. The shroud 23 is shown in FIG. 2A in the unfurled, or extended,condition, covering the umbilical cord 18 and the proximal portion ofthe probe handle 12. The grip 22 and the shroud 23 are constructed of athermally non-conductive material, such as a plastic. They should havesome flexibility to allow them to fit over the probe handle 12 and theumbilical cord 18. The sheath 20 also includes a hollow tubular catheter24 extending distally. The hollow catheter 24 is shaped and sized tocover the cannula portion 14 of the cryosurgical probe 10, preferablyfitting tightly over the probe cannula 14 to avoid interference with useof the probe 10 in a surgical environment. The hollow catheter 24 isconstructed of a thermally resistive material, such as a plastic, tofurther inhibit heat transfer from the surrounding tissues to the probecannula 14.

Attached to the distal end of the hollow catheter 24 is a thermallyconductive segment, such as a cap shaped tip 26. The sheath tip 26 isshaped and sized to fit snugly over the probe cold tip 16, to maximizethe transfer of heat through the sheath tip 26 to the probe cold tip 16.The sheath tip 26 can be a cap shaped element on the distal end of thecatheter 24 as shown, or it can be a thermally conductive segment shapedand located otherwise, to match the configuration and location of theprobe cold tip 16. The thermally conductive segment of the sheath, suchas sheath tip 26, must be constructed of a material which will readilytransfer heat, such as a metal. All of the components of the sheath 20are attached together in a sealing relationship, so that when the sheath20 is sterile, it covers the probe 10 in a protective envelope,rendering the probe 10 suitable for use in a surgical environmentVarious auxiliary instruments for use in conjunction with cryosurgerycan be mounted in the hollow catheter 24 or the sheath tip 26, as willbe explained below. These instruments can include temperature sensors,heaters, viewing optics, illumination optics, laser optics, andultrasonic transducers. Controls for operating these instruments, ordevices for displaying readings from these instruments, can be mountedin the probe handle 12 or elsewhere, for ease of observation and use bythe surgeon. Connections between the instrumentation near the sheath tip26 and the control devices in the probe handle 12 or proximal to thehandle 12 can be carried by the hollow catheter 24 as will be explained.

The sheath 20 can also include a connector body 28, which performsseveral functions. The connector body 28 provides a means for connectingthe hollow catheter 24 to the grip 22. It can also provide a means forlatching the sheath 20 to the probe 10. Further, the connector body 28can provide a mounting location for connectors, such as electricalcontacts or optical elements, to connect auxiliary instrumentation nearthe sheath tip 26 to the probe handle 12.

Finally, the connector body 28 can provide a mounting location for aport or fitting 30, such as a luer fitting, which can be used to providefluid flow to or from the area adjacent the sheath tip 26. Fluid flow tothe area can be required in some applications where fluid such as asaline solution must be injected into a body cavity having a smallopening. An example of such an application is insertion of the probecannula 14 into the uterus for endometrial ablation. Fluid flow to thearea around the tip 26, such as a saline solution or another fluidsuitable for irrigation of the area, can be provided by a syringeattached to the fitting 30. Alternatively, as shown in FIGS. 2B and 2C,a pliable saline reservoir 25 can be mounted on the grip 22 andconnected to the fitting 30 by a tube 27. Squeezing or depressing thesaline reservoir 25 can inject saline solution into the fitting 30. Theinjected fluid can be retained in the body cavity by sliding a plug (notshown) over the cannula 14 and the catheter 24 to fit snugly between thecatheter 24 and the opening of the body cavity. Similarly, a balloon(not shown) can be inflated around the catheter 24 to seal against thecavity opening. Fluid flow from the area around the tip 26 can beachieved by connecting a vacuum source to the fitting 30. Fluid flow canpass between the tip area and the fitting 30 via the hollow catheter 24,as will be explained below.

FIG. 2A also shows the finger stop 32 formed on the distal portion ofthe sheath grip 22, and the finger slide 34 formed on the proximalportion of the connector body 28. As will be shown below, the fingerslide 34 can be pulled toward the finger stop 32 to unlatch theconnector body 28 from the probe handle 12.

FIG. 3 shows the combined cryosurgical instrument 40 of the presentinvention, consisting of the sheath 20 disposed over the probe 10 as aprotective cover, having a thermally conductive segment for effectivelytransferring heat from the target tissue to the cold tip 16 of the probe10. It should be noted that the shroud 23 of the sheath 20 issufficiently flexible to stretch over the proximal end of the probehandle 12 and the umbilical cord 18.

FIG. 4 is a schematic drawing of the cryosurgical probe 10, in the styleof a longitudinal section view, to illustrate the components andfunctions of the typical probe 10 which can be incorporated into thepresent invention. A high pressure gas tube 36 provides a warm highpressure gas mixture to the refrigeration components in the probe 10,and a low pressure gas tube 38 receives the cool low pressure gasmixture returning from the probe 10. The high pressure and low pressuregas tubing 36, 38 is connected to the outlet and inlet, respectively, ofa gas compressor 42. The high pressure tube 36 is also connected to ahigh pressure passageway through a precooling heat exchanger 44, and thelow pressure tube 38 is connected to a low pressure passageway throughthe heat exchanger 44. The heat exchanger 44 precools the warm highpressure gas mixture by heat exchange with the cool low pressureexpanded gas mixture, before the high pressure gas is expanded at thecold tip 16.

A high pressure outlet 46 of the heat exchanger 44 is connected to ahigh pressure conduit 48 which passes through the hollow cannula 14 tothe cold tip 16. At the distal end of the high pressure conduit 48 is aJoule-Thomson expansion element 50, located in, or immediately adjacentto, the cold tip 16. High pressure cryogenic gas mixture passing throughthe high pressure conduit 48 is isenthalpically expanded by theexpansion element 50, to significantly lower the temperature of the gasmixture. The colder, low pressure gas mixture is then exposed to thecold tip 16, to cool the target tissue via the thermally conductivesheath tip 26. A separator plate 52 isolates the low pressure region ofthe cold tip 16 from the probe cannula 14. Low pressure gas mixturepasses back through openings in the separator plate 52 to return via theprobe cannula 14 to the low pressure inlet 54 of the heat exchanger 44.The flow of the low pressure gas mixture back through the cannula 14 canactually be via a low pressure conduit not shown in FIG. 4.

A female connector fitting 56 is provided in the distal portion of theprobe handle 12, to provide for a mating location between the probe 10and the sheath 20. An inwardly projecting latching flange 58 can beprovided around the outer perimeter of the female connector 56. One ormore connector elements 60 can be provided within the female connector56 for mating with auxiliary instrumentation carried by the sheath 20.The connector element 60 can be an electrical contact for use withauxiliary instrumentation such as a temperature sensor, a heater, or anultrasonic transducer. Similarly, the connector element 60 can be anoptical element for use with auxiliary instrumentation such as viewingoptics, illumination optics, or laser optics. The connector element 60is connected by way of an instrumentation conductor 62 to a display orcontrol device 64. The instrumentation conductor 62 can be an electricalconductor or an optical fiber bundle, as appropriate. Only one set ofconnector element 60, conductor 62 and display or control device 64 isshown, for the sake of simplicity, but it should be understood that aplurality of such systems could be used in any given cryosurgicalinstrument 40. Further, it should be understood that the display orcontrol device 64 could be located remotely from the instrument 40, suchas would be appropriate for a video optical viewing system. An alignmentrib 66 can be formed on the perimeter of the probe handle 12, to assistin alignment of the probe handle 12 with the sheath grip 22.

FIG. 5 shows that the connector body 28 has a longitudinal bore 68therethrough, to allow the passage of the probe cannula 14. The fitting30 is in fluid flow communication with the bore 68, to provide fluidflow to the exterior of the hollow catheter 24, which extends into thebore 68. A male connector fitting 70 is provided on the proximal portionof the connector body 28 to mate with the female connector fitting 56 inthe distal portion of the probe handle 12. A releasable latch 72 isprovided on the male connector fitting 70, to engage the latching flange58. One or more connector elements 74 are also provided on the maleconnector fitting 70 to engage the connector elements 60 within thefemale connector fitting 56 in the probe handle 12. Connection of theconnector element 74 to the auxiliary instrumentation, and connection ofthe fluid flow path from the fitting 30 to the hollow catheter 24 areshown better in a later Figure. FIG. 6 is an end view of the probehandle 12, showing the interior of the female connector fitting 56. Aplurality of connector elements 60 are shown arranged in a circle withinthe female fitting 56.

FIG. 7 shows the sheath 20 with the shroud 23 in the furled, orcontracted, condition. The sheath would normally be shipped and storedin this condition until disposition over a cryosurgical probe 10. Tabs78 are provided on the proximal end of the shroud 23 to assist inpulling the shroud 23 over the probe handle 12 and the umbilical cord18. FIG. 8 is a section view showing more detail of one embodiment ofthe sheath 20. An alignment groove 76 is shown in the inner bore of thesheath grip 22, to mate with the alignment rib 66 on the exterior of theprobe handle 12. It can be seen that the connector body 28 can beconstructed as a multi-piece assembly.

FIG. 9 shows more detail of one embodiment of the connector body 28 andits connection to the sheath grip 22. The connector body 28 comprisesessentially a distal section 80, an intermediate section 82, and aproximal section 84. The distal section 80 includes the finger slide 34,and the distal portion of the distal section 80 is attached to thehollow catheter 24. The intermediate section 82 is mounted within theproximal portion of the distal section 80, and it provides a means ofconnecting the distal section 80 to the instrumentation connectors 74and to the releasable latch 72. The intermediate section 82 can consistof a barrel 92 as shown, threaded to the latch 72. A collet 86 iscaptured between the barrel 92 and the latch 72. The collet 86 isattached to a sleeve 90 which is in turn attached to a connector fixture96. Instrumentation conductors 94 are connected to the instrumentationconnectors 74. The instrumentation conductors 94 pass through oralongside the longitudinal bore 68 to the catheter 24.

FIG. 10 shows more detail of one embodiment of the distal portion of thedistal section 80 of the connector body 28. The distal end of thelongitudinal bore 68 terminates in a fluid bore 100, which is in fluidflow communication with an internal bore 98 of the fitting 30. Theproximal portion of the hollow catheter 24 extends into the fluid bore100, with the diameter of the fluid bore 100 being larger than the outerdiameter of the catheter 24. This leaves a fluid flow space surroundingthe catheter 24 in the fluid bore 100. The proximal end 102 of the fluidbore 100 can be terminated by a shoulder in the longitudinal bore 68.Conversely, the proximal end 102 of the fluid bore 100 can be terminatedby an epoxy seal. The probe cannula 14 can fit snugly within thelongitudinal bore 68. The distal end of the connector body 28 can befitted with a strain relief collar 106 to fasten the catheter 24 to theconnector body 28. A space 108 within the collar 106 can be filled withepoxy to terminate the distal end of the fluid bore 100.

FIG. 11 shows a section view of the distal portion of the connector body28 and the proximal portion of the hollow catheter 24. In this view, itcan be seen that the catheter 24 is a multi-lumen catheter. A pluralityof lumens 110 pass longitudinally through the wall of the catheter 24.Some of the lumens 110 are used to conduct fluid flow, as shown at 112,and other lumens are used to conduct auxiliary instrumentation signals,as shown at 114. Within the fluid bore 100 only, the fluid lumens 112are open to the exterior of the catheter 24, while the fluid lumens 112along the remainder of the length of the catheter 24 are not open to theexterior. The instrumentation lumens 114 are closed to the exteriorthroughout the length of the catheter 24. Since the fluid lumens 112 areopen to the exterior within the fluid bore 100, fluid can flow from thefitting 30 into the wall of the catheter 24, or out of the wall of thecatheter 24 to the fitting 30. A central bore 116 passes through thecatheter 24 to accommodate the probe cannula 14.

FIG. 12A shows a transverse section view of the catheter 24 and theprobe cannula 14, forward of the connector body 28. The cannula 14incorporates a set of three coaxial stainless steel tubes 48, 55, 57,with the outer tube 57 fitting substantially snugly within the catheter24. It can be seen that a vacuum or insulation space 118 is formedbetween the outer tube 57 and a low pressure conduit 55. The lowpressure conduit 55 leads to the low pressure inlet 54 of the heatexchanger 44. The high pressure conduit 48 lies within the low pressureconduit 55.

FIG. 12B shows a transverse section view of an alternate embodiment ofthe catheter 24 and the probe cannula 14, forward of the connector body28. The cannula 14 incorporates a set of two coaxial stainless steeltubes 48, 55, with the outer tube 55 fitting substantially snugly withinan inner tube 117 in the catheter 24. It can be seen that a vacuumjacket or insulation space 118 is formed within the catheter 24, betweenthe inner tube 117 and the catheter 24. Here as before, the low pressureconduit 55 leads to the low pressure inlet 54 of the heat exchanger 44.The high pressure conduit 48 lies within the low pressure conduit 55.

FIG. 13 shows an elevation view of the distal end of the hollow catheter24 and the sheath tip 26. A plurality of ports 120 in the lumens 110 areformed in the distal end of the catheter 24. Some of the ports 120 arefor fluid flow to or from the area adjacent the sheath tip 26. Otherports 120 are for optical elements to support viewing, illumination, orlaser systems. Still other ports 120 could be used as connectionterminals for electrical connection to a temperature sensor, heater, orultrasonic transducer in the sheath tip 26.

FIG. 14 shows a longitudinal section of the distal portion of thecatheter 24 and the sheath tip 26. The auxiliary instrumentationconductor 94 passes through a lumen 114 to the distal end of thecatheter 24, at which point it connects to an optical element in theport 120, or to an auxiliary instrument 126 in the sheath tip 26. Theauxiliary instrument 126 could be a temperature sensor, a heater, atissue impedance measuring component, or an integrated component forperforming two or more of the temperature sensing, impedance measuring,and heating functions. For example, the instrument 126 could be acombination heater and resistance temperature detector (RTD) constructedof foil laminated between very thin (0.003 in.) sheets of polyimidefilm. Further, the auxiliary instrument could be an ultrasonictransducer. Those auxiliary instruments 126 which are in the sheath tip26 can be sandwiched between an inner thermally conductive layer 122 andan outer thermally conductive layer 124. The inner conductive layer 122can be made of copper, and the outer conductive layer 124 can be made ofstainless steel. If desired, epoxy can be injected between theinstrument 126 and the conductive layers 122, 124. An epoxy bleed hole128 in the outer layer 124 is provided for this purpose. If insulatinglayers are placed between the instrument 126 and the inner and outerlayers 122, 124, the insulating layers must be sufficiently thin toallow heat transfer therethrough. A thermally conducting grease 130 canbe provided within the sheath tip 26 to maximize the thermal contactbetween the probe tip 16 and the sheath tip 26.

FIG. 15 shows yet another embodiment of the sheath 220 of the presentinvention, in which one or more biasing elements in the catheterassembly 223 bias the conductive tip 226 of the catheter 224 against thecold tip 16 of the probe cannula 14. The sheath 220 includes a hollowgrip 222, into which a catheter assembly 223 is attachable. The catheterassembly 223 includes a catheter 224 and a connector body 228. Thesheath 220 can be attached to a cryosurgical probe handle represented inphantom, by means of one or more latches 225. The catheter 224 can beconstructed of a pliable material, such as an elastomer, which can bestretched, and which will be biased toward its unstretched length.Similarly, the connector body 228 can be constructed of a pliablematerial, such as an elastomer, which can be deformed, and which will bebiased toward its undeformed shape.

FIG. 16 shows a larger scale longitudinal section view of the distalportion of the grip 222 and the proximal portion of the catheterassembly 223. Also shown is an elevation view of the proximal portion ofthe cannula 14 of the cryosurgical probe 10. The connector body 228 hasa substantially tubular distal portion 231 which fits snugly into alongitudinal bore in the distal end of the hollow grip 222. The distalportion 231 of the connector body 228 can be held in a desiredlongitudinal position by one or more annular o-rings 227. The connectorbody 228 can also have a conical apron 233 on its proximal end, whichbears against the distal wall of the cavity within the hollow grip 222.The proximal end of the catheter 224 is attached within a longitudinalbore in the distal portion 231 of the connector body 228 by being gluedor otherwise bonded thereto. The seal between the catheter 224 and theconnector body 228, and the seal created by the o-rings 227, create asterile barrier at the distal end of the hollow grip 222.

The catheter assembly 223, including its conductive tip 226, is formedwith an undeformed length which is slightly less than the necessarylength to accommodate the length of the cannula 14, including its coldtip 16. Therefore, when the cryoprobe 10 is inserted into the sheath220, in order to latch the sheath 220 to the cryoprobe 10 handle, it isnecessary to slightly stretch or otherwise deform one or more componentsof the catheter assembly 223. The stretching or deformation in theembodiment shown can occur in the connector body 228, or in the catheter224, or in both. When the catheter assembly 223 has been deformed toaccommodate the length of the cannula 14, the elastic quality of thecatheter assembly 223 causes it to bias the conductive tip 226proximally against the cold tip 16 of the cryoprobe 10. This insures apositive contact between the conductive tip 226 of the catheter assembly223 and the cold tip 16 of the cryoprobe 10, thereby maximizing the heattransfer from the environment to the cryoprobe 10.

Rather than using elastic materials, a similar effect can beaccomplished by using other types of biasing elements, such as one ormore springs (not shown), to bias the catheter assembly proximally,without departing from the spirit of the present invention. Further, theconductive tip 226 or the cold tip 16, or both, can be slightly taperedto increase the positive contact area between the two tips.

While the particular invention as herein shown and disclosed in detailis fully capable of obtaining the objects and providing the advantageshereinbefore stated, it is to be understood that this disclosure ismerely illustrative of the presently preferred embodiments of theinvention and that no limitations are intended other than as describedin the appended claims.

We claim:
 1. A sheath for use as a removable cover for a cryosurgicalprobe, said sheath comprising: a hollow grip removably attachable to acryosurgical probe; a thermally resistive catheter assembly attachableto said hollow grip, said catheter assembly having a tubular passagewayfor receiving a cannula portion of a cryosurgical probe; a thermallyconductive segment on said catheter assembly, said conductive segmentbeing in thermal contact with a heat transfer portion of a cryosurgicalprobe, when said catheter assembly is disposed over a cannula portion ofa cryosurgical probe; and a biasing element on said catheter assembly,said biasing element being constructed to longitudinally bias saidconductive segment of said catheter assembly against a heat transferportion of a cryosurgical probe when said hollow grip is attached to acryosurgical probe.
 2. A sheath as recited in claim 1, wherein saidbiasing element comprises an elastic material.
 3. A sheath as recited inclaim 1, wherein said catheter assembly comprises: a connector bodyattachable to said hollow grip; and a catheter attached to saidconnector body.
 4. A sheath as recited in claim 3, wherein saidconnector body comprises said biasing element.
 5. A sheath as recited inclaim 4, wherein said connector body comprises an elastic material.
 6. Asheath as recited in claim 3, wherein said catheter comprises saidbiasing element.
 7. A sheath as recited in claim 6, wherein saidcatheter comprises an elastic material.
 8. A sheath as recited in claim3, wherein said catheter and said connector body, in combination,comprise said biasing element.
 9. A sheath as recited in claim 8,wherein said catheter and said connector body comprise elasticmaterials.
 10. A cryosurgical instrument, comprising: a probe handle; aprobe cannula attached to said probe handle; a heat transfer element onsaid probe cannula; a cooling system providing a coolant at a desiredtemperature adjacent said heat transfer element; a hollow grip removablyattachable to said probe handle; a catheter assembly attachable to saidhollow grip, said catheter assembly having a tubular passageway forreceiving said probe cannula; a thermally conductive segment on saidcatheter assembly, said conductive segment being in thermal contact withsaid heat transfer element, when said catheter assembly is disposed oversaid probe cannula; and a biasing element on said catheter assembly,said biasing element being constructed to longitudinally bias saidconductive segment of said catheter assembly against a heat transferportion of a cryosurgical probe when said hollow grip is attached to acryosurgical probe.
 11. A cryosurgical instrument as recited in claim10, wherein: said probe cannula is inserted in a distal direction intosaid catheter assembly; and said biasing element generates a proximallydirected bias against said conductive segment of said catheter assembly.12. A cryosurgical instrument as recited in claim 11, wherein insertionof said probe cannula into said catheter assembly and attachment of saidhollow grip to said probe handle axially stretches said biasing elementto create said proximally directed bias.
 13. A cryosurgical instrumentas recited in claim 12, wherein said biasing element comprises acatheter in said catheter assembly.
 14. A cryosurgical instrument asrecited in claim 13, wherein said catheter comprises an elasticmaterial.
 15. A cryosurgical instrument as recited in claim 12, whereinsaid biasing element comprises a connector body in said catheterassembly.
 16. A cryosurgical instrument as recited in claim 15, whereinsaid connector body comprises an elastic material.
 17. A cryosurgicalinstrument as recited in claim 12, wherein said biasing elementcomprises a catheter and a connector body, in said catheter assembly.18. A cryosurgical instrument as recited in claim 17, wherein saidcatheter and said connector body comprise elastic materials.
 19. Asheath for use as a removable cover for a cryosurgical probe, saidsheath comprising: a hollow grip removably attachable to a cryosurgicalprobe; a connector body attachable to said hollow grip; a thermallyresistive catheter attached to said connector body, said catheter havinga tubular passageway for receiving a cannula portion of a cryosurgicalprobe; and a thermally conductive segment on said catheter, saidconductive segment being in thermal contact with a heat transfer portionof a cryosurgical probe, when said catheter is disposed over a cannulaportion of a cryosurgical probe; wherein said sheath is constructed tocause attachment of said hollow grip to a cryosurgical probe to resultin a heat transfer portion of the probe pushing in a distal directionagainst said conductive segment of said catheter thereby stretching atleast one of said catheter and said connector body, and therebylongitudinally biasing said conductive segment against the heat transferportion of the cryosurgical probe.